Hi Peter,

Start with a cleared variable; for every keypush, multiply the value in the variable by 10 & add the new value to it. If you are always entering 5 digits, there's no need for the #.
Debouncing is another problem - allow a delay of 100 to 125mS between key scans (humans are slow devices!), & use a state machine to wait for a key on, then for all keys off.

Like many things in life, it's easier the second time!

Regards,

Richard